Bi-static circularly symmetric retrodirective antenna

ABSTRACT

A circularly symmetric antenna system capable of providing retro-directive retransmission of a modulated or an encoded incident signal, or having the ability of being employed as a bistatic relay where retransmission may be directed from the initiating station. Also the system may be used to provide selective automatic suppression of a retransmission in an unwanted direction.

United States Patent [1 1 Coleman Aug. 21, 1973 [54] BI-STATIC CIRCULARLY SYMMETRIC 3,255,450 6/1966 Butler 343/100 TD RETRODIRECTIVE ANTENNA 3,305,864 2/ 1967 Ghose 343/100 TD 3,680,112 7/1972 Thomas 343/100 TD [75] Inventor: H. Paris Coleman, Alexandria, Va.

[73] Assignee: The United States of America as Primary Examiner-Benjamin A. Borchelt represented by the Secretary of the Assistant Examiner-Richard E. Berger Navy, Washington, DC. Attorney-R. S. s ciascia, Arthur L. Branning et al. [22] Filed: Feb. 25, 1972 21 Appl. No.2 229,368 [57] ABSTRACT A circularly symmetric antenna system capable of pro- [52] us CL 343/100 TD 325/14 343/854 viding retro-directive retransmission of a modulated or 511 Int. Cl. ..mi1 15/14 incident signal, having the ability 58 Field of Search 343/100 TD 854- being Y as a relay Where retransmis- 5 sion may be directed from the initiating station. Also the system may be used to provide selective automatic [56] References Cited suppression of a retransmission in an unwanted direc- UNITED STATES PATENTS 3,196,438 7/1965 Kompfner 343/100 TD 5 Claims, 2 Drawing Figures RECEIVER RECEIVER 2 8 (so 2 PHASE DETECTOR I PROCESSOR {i} l PROCESSOR J i mm 1 i l I l l TRANSMITTER i l l l 40 i; POWER DlVlDER PAIENIEBmse; ms 3754257 sum 1 or 2 F T T MULTI MODAL NETWORK I II II 0 I I? I l l I l TRANSPONDING I CIRCUITY u b I l I l L 1 RECEIVER PROCESSOR 'll-Iv TRANSMITTER POWER DIVIDER I'll H RECEIVER PROCESSOR PATENIEU MIBZI I973 FIG. 2.

Ill-STATIC CIRCULARLY SYMMETRIC RETRODIRECTIVE ANTENNA STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF INVENTION Automatically retrodirective arrays have in general either been restricted to linear or planar arrays such as the Van Atta array (U. S. Pat. No. 2,908,002) or a modified array which requires the fitting of complex circuitry to each element in the array.

The Van Atta array lacks the capability of operating with a circularly symmetric array, is unable to provide 360 coverage, and cannot be used with continuous aperture antenna systems. On the other hand, the modified array is relatively expensive, and an effort must be made to assure that all circuits are identical to each other in order to provide a symmetrical response.

Another problem in the antenna art is the design of a bi-static relay which may be used for relaying a communication from one station toward a different station where the angle of the retransmitted signal can be controlled from the initiating station.

Finally, a further problem in the antenna art is the selective automatic suppression of a retransmission in an unwanted direction. Such a device is useful in many areas but the primary application is in the field of aviational navigation.

Considering such drawbacks I have developed a circularly symmetric antenna system which is capable of being used in all three of the above areas and characteristically may provide retrodirectivity, be employed as a bi-static relay, as well as being capable of selected automatic suppression in unwanted directions.

SUMMARY The proposed system may include the multimodal circularly symmetric antenna system described in my copending application, Ser. No. 220,663, filed Jan. 25, 1972. The detailed theory presented therein applies in part to this system, and for simplicity of description the operation will be described when only modes '7 and l" are utilized. Other mode pairs, or more than one mode pair, may be utilized however by following the teachings herein. I

The basic antenna system as described in my co pending application may be modified and adapted to provide, among other things, two receivers at the mode terminals of a multimodal network. The phase difference between mode 0 and mode 1 corresponds directly to the angle of the signal arrival. A processor decodes the information and then it is applied to a memory so as to store the value of the incoming angle or other in formation. The output of the memory sets an output line phase shifter (if desired) and the signal is subsequently passed back through the multi-modal network to the antenna for retransmission. By including a second processor detection, modulation or frequency translation may be provided.

OBJECTS It is therefore an object of this invention to provide a retrodirective circularly symmetric antenna system capable of retransmitting in a direction which is determined by the direction of arrival of an encoded signal.

Another object of this invention is to provide a bistatic relay wherein the direction of the reradiated transmission can be directed from the initiating station.

A further object of this invention is to provide selective automatic suppression of a retransmission in unwanted directions.

Other objects of the invention will be readily apparent to those skilled in the art by referring to the following detailed description when considered in conjunction with the accompanying drawing wherein like parts are similarly labeled throughout.

THE DRAWING FIG. 1 shows the fundamental components required to provide directional transponding of an encoded signal;

FIG. 2 is a diagram of the transponding circuitry required to provide a modulated or encoded signal.

DETAILED DESCRIPTION Referring to FIG. 1, the system includes circular antenna system 10, interconnecting lines 12, multimodal feed network 14, mode terminals 16, and transponding circuitry 17.

The antenna 10 may be of a multitude of types as described in my co-pending application. Essentially however any type of antenna system 10 which has the capability of propagating progressively linearly varying phase functions around the entire periphery in the far field region, is acceptable as an antenna system.

The interconnecting lines 12 are employed so as to provide a connection between antenna system 10, and the feed network 14 and therefore are chosen as a result of the particular selection of the antenna system and feed network. For example, if the antenna system 10 consists of a bi-conical horn, the interconnecting line could well be either a coaxial line or a circular waveguide. The bi-conical horn may be driven by any method acceptable and well known in the art including that disclosed by R.C. Honey in the Proc. IRE, Vol. 45, Oct. 1957, pp. 1374-1383. Similarly if an N element array is selected as an antenna system 10, the interconnecting line could consist of N number of coaxial cables, each connected to an element terminal of a Butler matrix. The selection of any particular interconnecting line 12 is unimportant to the operation of the entire system as long as the interconnecting line 12 is capable of accurately maintaining amplitude and phase relationship information between the antenna system 10 and the feed network 14.

The feed network 14 is responsible for creating a progressive change in phase of energy at a constant radius in the far field. If a point at a fixed radius in the far field is allowed to vary in angle 4) with respect to antenna 10 as shown in FIG. 1, the network must provide a particular phased signal at any particularly defined angle d).

Consider a source of signal applied to a particular mode terminal 21 of the feed network 14. As d: is swept around the periphery in a counterclockwise direction starting from 0, the phase of the signal increases from 0 to 360 or multiples of 360 as the 4: revolution is complete. That is, when it returns to 360, a particular phased mode is established around the antenna.

The particular mode which is being energized may be determined by measurement taken in the far field. This is accomplished by noting the number of times the signal increases in phase by 360 as b varies from to 360. For example, if 45 is swept from 0 to 360 and the value of the phased signal remains at 0 around the entire periphery, mode 0 is present. If however, (I) is varied from 0 to 360 and the value of the phased signal correspondingly changes from 0 and 360, mode 1 is present.

For simplicity of description, the operation of this invention will be described where only modes 0 and l are utilized. Other mode pairs, or more than one mode pair may be utilized however, by merely following the teachings regarding mode 0 and mode 1.

Referring again to FIG. 1, when an incident plane wave, with an angular frequency a, is presented to the antenna from a direction of (1),, the signal on line 20, (0 mode terminal) is in the form:

S A, exp [-j w t] while the signal at the 1 mode terminal (line 21) is in the form:

1= 1 p Liq ol p [-iw] Comparing Eq. (1) with Eq. (2) or mode 0 with mode I, it can be seen that phase difference corresponds directly to the angle of arrival, namely Thus the phase difference, present upon lines 20 and 21 provides a .detectable difference in phase between the modes and gives a direct indication of the angle of arrival.

Referring to FIG. 2, lines 20 and 21 are correspondingly fed through circulators 22 and 24 to the respective receivers 26 and 28. The outputs of the receivers are applied to phase detector 30 which detects the original angle of arrival (1),. The signal from receiver 26 is also applied to processor 32. Processor 32 is provided to decode incoming information such as codes that identify the source of an incident signal or codes that supply system instructions. The decoded information is then applied to digital processor 34. For example, since processor 34 receives the angle from the phase detector 30 by way of A/D converter 35 a displacement angle A4), may be decoded by processor 32 and passed on to processor 34.

Processor 34 may derive a digitally encoded value for a bi-static relay. For example, the incoming signal may have information therein as to the direction in which it is to be retransmitted. Assume the signal is to be retransmitted at (1:, (b, Ada. The phase detector 30 supplies A/D converter 35 with the d), information, and is then applied to processor 34 in digital form. The A4: value which was encoded in the received signal is decoded by processor 32 and also applied to processor 34. Thus the output of processor 34 is capable of controlling phase shifter 40 to provide a phase shift of Generally speaking, processor 32 may provide information detection, modulation or other similar function and not merely restricted to decoding functions.

An additional output from processor 32 is coupled to transmitter 36. The transmitter 36 may, among other things, provide frequency translation at this point.

The output of the transmitter is split into two parts by a power divider network 38. The first part goes back to terminal 0 of the feed network 14 by way ofa circulator such as 22 or an equivalent device. The second part goes through the phase shifter 40 and finally to terminal l of the feed network 14 in a manner similar to the first part. In order to assure accurate bi-static control or retrodirectivity, the phase properties between points 42 and 44 and their respective circulators 22 and 24 must be maintained. For example to accomplish this lines 43 and 45 may be of an equal electrical length.

The output of the circuit at point 42 is in the form:

S, G, exp [jw,t]

3 where G, is the gain of the mode 1 portion of the circuit 17 and w, is an angular frequency established by transmitter 36. The output of the circuit at point 44 is in the form:

where G, is the gain of the mode 0 portion of the circuit 17.

The far field radiation from the antenna on mode 1 therefore is:

E, G, A, exp [-jm,t] exp Lida] while the far field from mode 0 is A. p l-v' i p m4 A M It should be noted that for 41 41,, A d), in Eq. (5) and Eq. (6), the far field radiation from the two modes is in phase, thus a beam will radiate in this direction. The pattern as shown in Eqs. (5) and (6) is of course taken in the plane normal to the longitudinal axis of the antenna system 10, and the usual terms involving distance are omitted.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. For example, the teachings described herein regarding electromagnetic waves equally applies to the analogous structure in acoustics. Suppressing a transmission in an unwanted direction may be accomplished by inhibiting the transmitter 36 in certain sectors. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. What is claimed and desired to be secured by letters patent of the United States is:

l. A transponding circularly summetric antenna system comprising:

circularly symmetric antenna means for receiving an incident signal arriving at a particular angle;

multimodal network means having pairs of mode terminals, said network means being coupled to said antenna means;

transponding means coupled to a selected pair of said mode terminals for manipulating said signal; connecting means for applying said manipulated signal to said selected pair of said mode terminals whereby said manipulated signal is transmitted from said antenna means at a selected angle.

a first and second receiver;

said first receiver being connected to a first mode of said mode pair and said second receiver being connected to a second mode of said mode pair;

phase detection means connected to said receivers for detecting the angle of the incident signal;

a first processor means coupled to said phase detector means for controlling a phase shifter;

whereby said phase shifter and said processor are able to control the angle of retransmission.

* IF t 

1. A transponding circularly summetric antenna system comprising: circularly symmetric antenna means for receiving an incident signal arriving at a particular angle; multimodal network means having pairs of mode terminals, said network means being coupled to said antenna means; transponding means coupled to a selected pair of said mode terminals for manipulating said signal; connecting means for applying said manipulated signal to said selected pair of said mode terminals whereby said manipulated signal is transmitted from said antenna means at a selected angle.
 2. The system as claimed in claim 1 wherein said multimodal network means comprises: a Butler matrix.
 3. The system as claimed in claim 2 wherein said selected pair of mode terminals comprise: mode 0 and mode
 1. 4. The system as claimed in claim 1 wherein circulator means are disposed between said transponding means and said mode terminals.
 5. The system as claimed in claim 1 wherein said transponding means comprises: a first and second receiver; said first receiver being connected to a first mode of said mode pair and said second receiver being connected to a second mode of said mode pair; phase detection means connected to said receivers for detecting the angle of the incident signal; a first processor means coupled to said phase detector means for controlling a phase shifter; whereby said phase shifter and said processor are able to control the angle of retransmission. 